Beam deflection type electron discharge device



March 14, 1961 M. B. KNIGHT ,9 5,3

BEAM DEFLECTION TYPE ELECTRON DISCHARGE DEVICE Filed Jan. 17. 1958INVENTOR. MARK B. KNIGHT United States Pateti't G BEAM DEFLECTION TYPEELECTRO DISCHARGE DEVICE Mark B. Knight, West Caldwell, N.J., assignorto Radio I Corporation of America, a corporation of Delaware 7 FiledJan. 17, 1958, Ser. No. 709,565 14 Claims. (cl. 313-82) This inventionrelates to beam deflection type electron tubes and particularly to thosein which the electron beam is deflected to selectively divide beamimpingement viding'a sheet electron beam; one or two conventional gridelectrodes adjacent the cathode and disposed transversely of thebeampath; a pair of imperforate beam de-.

flection plates, one extending along. the sheet beam on either sidethereof; and a pair of anode plates disposed substantially transverselyof the sheet beam at the end i of the. deflection plates remotefrom thecathode. While providing the general advantages inherent-to beamdeflection type electron tubes as mentioned above, such prior art tubeshave lacked reasonably good sensitivity and have been subject toelectron impingement on the deflection plates. As is well known, thelatter is undesirable in that output current is undesirably decreased orotherwise adversely affected due to many of the electrons failing toreach the anode. Also, harmful loading of the signal input circuitresults giving an attendant loss of A.C. power and a lower Q in thosecases where selective circuits are connected to the deflection plates.

In order to achieve some reasonable measure of sensitivity, priorarttubes have, by necessity, relied upon selectively dividing a sharplyfocused beam between closely abutting or overlapped anode platesdisposed in the central beam path at the focus point of the beam. Thus,a given deflection of the sharply focused beam produces a maximum changeof output signal for the given prior an electrode structure. However,even with skilled design of electrodes for sharp beam focus, sensitivityof prior art tubes having beam currents as high as a few milliamperes islow.

Basic electrostatics theory would suggest that sensitivity couldotherwise be improved in such prior art tubes focus for obtainingsensitivity, the loss of such focus tends to cancel the advantage ofreduced electron beam velocity. It the beam deflection plates arelengthened or are placed closer together in an attempt to achievegreater sensitivity, electron impingement upon: these plates isincreased giving the attendant harmful efiects thereof.

Providing a sufliciently negative bias voltage on the deflection platesin order to prevent electron impingement during peak excursions of thesignal voltage is impractical because such a measure makes it diflicult,if not impossible, to obtain electron beam flow past the deflectionplates to the anodes.

It is therefore an object of my invention to provide an improved beamdeflection type of electron tube having high sensitivity and beinggenerally devoid of the undesirable characteristics enumerated above.

Briefly, according to my invention, a beam deflection type electron tubeincludes means for providing a sheet electron beam, e.g., an elongatedcathode and electron beam accelerating grid. A pair of anode plates aredisposed one on either side of the beam and extend generally therealoug.One of a pair of foraminous beam deflection grid electrodes is disposedsubstantially coextensive with each anode plate intermediate that anodeplate and the electron beam. In operation, the electron beam isdeflected by the foraminous deflection electrodes away from a centralpath through one or the other of said foraminous deflection electrodesand onto an adjacent anode plate.

In the drawings:

Fig. 1 is a schematic plan view in section of the electrode cage portionof an electron tube illustrating the basic concepts according to myinvention;

Fig 2 is an elevation view partly in section of the device of Fig. 1taken along line 2-2 of Fig. 1; I

Fig. 3 is a schematic transverse sectional view of the electrode cageportion of an electron tube according to modification of my invention;

Fig. 4 is a cut-away perspective view of a preferred embodiment of myinvention;

Fig. 5 is a view in cross-section of the device of Fig. 4 taken alongline 5-5 of Fig. 4; and

Fig. 6 is a fragmentary sectional view illustrating a modification ofthe device of Figs. 4 and 5.

Referring to Figs. 1 and 2, an electron tube 10 is shown illustratingthe basic concept of my invention. The tube 10 comprises an envelope 12enclosing an electrode cage including an elongated cathode 14 having anelectron emissive coated surface 16. An electron accelerator grid 15 isdisposed adjacent the cathode 14 coextensive with the emissive surfacethereof. The cathode-accelerator grid arrangement 14-15 is adapted toprovide a sheet beam of electrons directed in a path away from andgenerally perpendicular to the emissive surface 16. A pair of sheetmetal anode plates 18 are disposed one on either side of the beam pathand extend therealong. A pair of foraminous electron beam deflectiongrid electrodes 20 are disposed between the anode plates 18 with eachgrid substantially coextensive with an adjacent one of said anode platesand disposed intermediate that anode plate and the beam path. Theforaminous deflection electrodes 20, as illustrated, comprise planarparallel-wire structures. These electrodes may, however, comprise anysuitable perforate grid structure known to the art, e.g., wire mesh.Also, as suggested in the preceding brief description of my invention,some conventional means other than the cathode and accelerator gridarrangement 14-15 may be used to provide the desired electron beam.Moreover, this beam need not be of sheet form, but is made so only as anexpedient of available power.

With such an electrode disposition, electrons emitted from the cathode14 pass through the accelerator grid 15 and centrally along and betweenthe two foraminous deflection electrodes 20 when these two electrodesare operated at the same electrical potential. When a potentialdiiference is applied to the foraminous deflection -electrodes 20, theelectron beam is deliberately deflected from the straight central pathbetween these electrodes and caused to pass through one or the other ofthem and to impinge on the anode plate 18 adjacent thereto.

Analyzing the theoretical operation of the device 10, it will beapparent to one skilled in the art that many of the disadvantagesinherent with prior art beam deflection tubes is avoided. For example,according to my' in vention, as schematically illustrated in Fig. 1, itis possible to operate the tube It with a negative bias on thedeflection electrodes 20. This is'generally not practical in tubes ofprior art design since there a negative bias on the deflectingelectrodes prevents passage of the electron beam past the deflectionplates and onto the anodes. In the tube according to my invention suchis not the case since the potential on the anode plates 18 provides apositive field whose influence is felt in the space between theforaminous deflection electrodes 20 notwithstanding the negative 'biasthereon. This, of course, is possible due to the foraminous nature ofthe deflection electrodes according to my invention; Furthermore, eventhough the beam is deliberately deflected into the foraminous deflectionelectrodes 20, and even though these electrodes may have aninstantaneous positive potential on them, electron impingement is at aminimum.

As will be readily appreciated, beam focus per se is not a fundamentalrequirement for beam deflection type tubes. Rather, this measure wasused by the prior art only to obtain some degree of sensitivity. Since,according to my invention, sensitivity is not directly dependentuponbeam focus as it is in prior art tubes, limitations present in priorartdesigns are nonexistent or less severe in my invention. This meansthat according to my in vention sensitivity maybe improved by themeasures-hereinbefore mentioned which could not be applied to the priorart designs. For example: beam velocity may be decreased; the deflectionelectrodes may be lengthened; or the deflection electrodes may bepcsitioned closer together.

Fig. 3 illustrates an electron tube 30*, according to a modification ofmy invention. The tube 30 comprisesan envelope 32 enclosing an electrodecage including a cathode 34 having an electron emissive coated surface36, a control grid 38 adjacent the cathode 34, and an accelerator grid40 adjacent the control grid 38. Both the control grid 38 and theaccelerator grid 40 are disposed substantially coextensive with thecathode emissive surface 36. A pair of anode plates 42 anda pair offoraminous beam deflection grid electrodes 44 (e.-g., parallel cerealswire structures) are provided similar to the anode plates andforam-inous. deflection electrodes 18 and 20- respectively of tube 10,except that they are spaced closer together at their ends remote fromthe cathode than they are at their ends adjacent the cathode.Theelectrodes of the tube 30 are elongated in a direction as illustratedinto and out of the paper similar to the electrodes of tube. 10 in orderto utilize the advantages of'a sheet electron beam.

The V-like arrangement of the anode plates and foraminous deflectionelectrodes 42 and 44, respectively, serves to provide an even moresensitive deflection control. In this arrangement, as in the tube 10, agiven deflection signal will produce a given amount of beam deflection,but the amount of beam deflection necessary to cause the beam to passthrough one of the foraminous deflection electrodes 44 and onto itsadjacent anode 42 is less than would be necessary in a'parallelarrangement such as illustrated in. Fig. 1. In addition any adverseeffects of the undeflected beam completely passing the anode plates andforaminous'deflection electrodes is reduced.

Figs. 4 and 5 illustrate an electron tube 60 according to a preferredembodiment of my invention. The tube 60 comprises an envelope 62enclosing an electrode cage structure. An elongated cathode 64 isprovided with an electron emissive coating 66 on one surface thereof,Conventional wire-wound half grids 68 and 17.0 are. disposed adjacent toand substantially coextensive with. the

emissive surface 66 of the cathode 64. The half grids 68 and 70 serverespectively as a control grid and an accelerator grid. Such a cathodeand grid arrangement is adapted to provide a sheet beam ofelectronsalong a path generally perpendicular .to and away from the coatedsurface 66 of the cathode 64.

A V-like disposition of'anode plates 72 and foraminous deflection gridelectrodes 73 opening toward the cathode 64 is provided somewhat similarto the arrangement of the anode plates 42 and foraminous deflectionelectrodes 44 of tube 3%, excepting that a foraminous deflectionelectrode 73 does not lie parallel to its adjacent anode plate 72.Rather, eachyforaminous deflection electrode 73 and its adjacent anodeplate 72 are disposed closer together at their ends remote fromthecathode 64 than at their ends adjacent the cathode 64. Statedotherwise the V angle formed by the anode plates 72 is greater than theV angle formed by the deflection grid electrodes 73. A plurality: oflead-ins 74 are provided through one end of the envelope 62 to permitapplication of suitable electrical potentials to the electrodes therein.

In the tube 60 the use of conventional wire-wound half grids for theforaminous deflection electrodes 73 permits the relatively heavy siderods 75 at the end remote from the cathodeto be disposed out and awayfrom the central, no-deflection-signal beam path. With the forarninousdeflection electrode side rods 75 soshielded the anode plates 72,electron reception therebyis practically eliminated.

The'tube 60. also includes a sheet metal tubular shield 76 snrrounding the tube electrodes. The shield 76 serves to reduce certaininterelectrode capacitances, to shield the tube electrodes from externalmagnetic fields, and to prevent any of theelectron beam from passingcompletely past the anode plates '72 via a central beam path. Merelyoperatingthe. shield, 76 at; cathode potential provides a substantiallycomplete. reflector to" electrons tending to follow a central beam paththrough the. opening between the anode plates 72 at the end remote fromthe cathode. Howevena more effective reflection of the beam can beachieved according to the structure illustrated in Fig. 6.

Big. 6 shows a modification of the shield 76 of Figs. 4 and 5 which canbe incorporated in place of the shield 76 thereof. According to Fig. 6 ashield 80 is provided which includes a re-entrant portion 82 at the endthereof remote, from the cathode. The re-entrant, portion 82 iscontoured, along the, ends of the foraminous deflection electrodes '73such. that it extends] closely adjacent he 'e ds' f he anode'pl tes 72.Sucha ge me ric disposition; or; the end or the shield 80 provides amore effective, reflection of electrons by returning the electrons whichpass the anode plates 72 back-toward these plates in trajectories whichare less likely to encounter the dcfiection electrode side rods 75;

According, to a preferred: practice of my invention, the,various'electrodes' are so dimensioned and disposed as to provide forthe formation of a properly directed sheet electron beam which tendstoconverge at the far endsof the anode plates.. Accordingly, oneexperimental tube2 design constructed according to Figs. 4 and 5 had thefollowing dimensions and relative disposition.

(a) A control grid 68 of 2 mil wire, 'turns per inch,

and mil distance between side rods.

(12) An accelerator grid 70 of- 2.5 'mil wire, 72 turns per I inch, and220 mildistancebetween side rods.

(e);;Fe1-aminous deflection electrodes74 of 2 mil wire,'Zflturnsper'inch, and 400 mil distance between side rods.

(it) Length; of anode plate; 72 asviewed in Fig. 5, 340

mils.

(2}) Width of, cathode 64; (extentalong control grid 68 asyiewedin Fig-5). 8 .111ils. Y

(f), Spacing between, cathode 64, and. control, grid 68', 6

76 j mils. Y

(g) Spacing between control grid 68 and accelerator grid 70, 16 mils.

(h) The V angle disposition of anode plates 72, 10.2. (i) The .V angledisposition of foraminous deflection electrodes 74, 85. (j) Spacingbetween the two anode plates 72 at the ends adjacent cathode 64, 150mils.

(k) Spacing between the two foraminous deflection electrodes 74 at theends of the planar portion thereof adjacent cathode 64, 120 mils.

(l) Spacing between the two anode plates 72 at the ends remote fromcathode 64, 36 mils.

(m) Spacing between the two foraminous deflection electrodes 74 at theends of the planar portion thereof remote from cathode 64, mils.

(n) Spacing between cathode 64 and anode plates 72,

1 55 mils.

(0) Spacing between cathode 64 and foraminous deflection electrodes 74,125 mils.

(p) Spacing between a foraminous deflection electrode 74 and itsadjacent anode plate 72 at the end adjacent cathode 64, mils.

(q) Spacing between a foraminous deflection electrode 74 and itsadjacent anode plate 72 at the end remote from cathode 64, 10 mils.

It will be appreciated that various. modifications can be made accordingto my invention. For example, conventional screen and suppressor gridscan be added between each of the foraminous deflection electrodes 74 andits adjacent anode plate 72. This and other modifications will bereadily suggested to one skilled in the art.

Y What is claimed is: i

1. An electron tube of the beam deflection type comprising means forproviding a single beam of electrons generally along a predeterminedpath; a pair of anode plates disposed in substantially mutual facingrelationship on opposite sides of said predetermined path; and a pair ofseparate foraminous electron beam deflection grid electrodes disposedsubstantially coextensive with said anode plates and adapted to have anelectric signal applied between them, each of said foraminous deflectionelectrodes being intermediate a different one of said anode plates andsaid predetermined path.

2. A beam deflection type electron tube comprising a pair of anodeplates in substantially facing relation to each other; a pair ofseparate foraminous electron beam deflection grid electrodesintermediate said anode plates and substantially coextensive therewithand adapted to have an electric signal applied between them; a cathodedisposed adjacent one end of said anode plates and having an emittingsurface facing along a predetermined path intermediate said foraminousdeflection electrodes; and an electrode adjacent said emitting surfaceand adapted to accelerate electrons emitted by said emitted surfacealong said predetermined path.

3. A beam deflection type electron tube comprising a cathode having anemitting surface for generating electrons adapted to be beamed generallyalong a single predetermined path; a pair of anode plates disposed oneon either side of said predetermined path and extending generallytherealong in facing relation to each other; a pair of separateforaminous electron beam deflection grid electrodes adapted to have anelectric signal applied between them, each disposed adjacent to andsubstantially coextensive with a different one of said anode plates andintermediate said adjacent anode plate and said predetermined path.

4. An electron tube of the beam deflection type comprising a cathodehaving an emitting surface facing generally along a predetermined path;a pair of anode plates, one disposed on either side of saidpredetermined path and extending therealong facing said predeterminedpath, said cathode being disposed adjacent one end of said pair of anodeplates, said anode plates being spaced further apart at said one endthan at the end remote from said one end; and a pair of separateforaminousfelectron beam deflection grid; electrodes disposed betweensaid anode plates substantially coextensive therewith and adapted tohave an electric signal applied between them, one on either side of saidpredetermined path.

5. An electron tube of the beam deflection type comprising a cathodehaving an emitting surface facing generally along a predetermined path;a pair of anode plates, one disposed on either side of said given pathand extending therealong facing said predetermined path, said cathodebeing disposed adjacent one end of said pair of anode plates, said anodeplates being spaced further apart at said one end than at the end remotefrom said one end; and a pair of separate foraminous electron beamdeflection grid electrodes disposed between said anode platessubstantially coextensive therewith one on either side of saidpredetermined path, each of said foraminous deflection electrodes beingspaced further from its adjacent anode plate at said one end thereofthan at said end remote from said one end, said cathode, anode plates,and deflection grid electrodes forming a structure symmetrical aboutsaid path.

6. A beam deflection type electron tube comprising: a cathode having anemitting surface facing generally along a predetermined path; a pair ofanode plates spaced from each other in a V-like arrangement, each ofsaid anode plates being disposed on opposite sides of and along saidpredetermined path away from said cathode with the V thereof openingtoward said cathode; and a pair of separate foraminous electron beamdeflection grid electrodes spaced fro-m each other in a V-likearrangement, said pair of foraminous deflection electrodes beingdisposed substantially between said anode'plates on opposite sides ofsaid predetermined path with the V thereof opening toward said cathode,each of said foraminous deflection electrodes being substantiallycoextensive with .its adjacent anode plate, the V of said foraminousdeflection electrodes being more acute than the V of said anode plates.

7. An electron tube of the beam deflection type comprising a cathodehaving an emitting surface facing generally along a predetermined path;at least one grid electrode disposed adjacent said cathode transverselyof said predetermined path; a pair of anode plates disposed on theopposite side of said at least one grid electrode from said cathode insubstantially mutual facing relationship on opposite sides of saidpredetermined path; and a pair of separate foraminous electron beamdeflection grid electrodes disposed substantially coextensive with saidanode plates, each of said foraminous deflection electrodes beingintermediate a different one of said anode plates and said predeterminedpath.

8. An electron tube of the beam deflection type comprising an electrodecage including a cathode having an emitting surface facing generallyalong a predetermined path; a pair of anode plates, one disposed oneither side of said given path and extending therealong facing saidpredetermined path, said cathode being disposed adjacent one end of saidpair of anode plates, said anode plates being spaced further apart atsaid one end than at the end remote from said one end; at least one gridelectrode disposed intermediate said cathode and said pair of anodeplates transversely of said predetermined path; and a pair of separateforaminous electron deflection grid electrodes disposed between saidanode plates substantially coextensive therewith, one oneither side ofsaid predetermined path.

9. An electron tube of the beam deflection type comprising a cathodehaving an emitting surface facing generally along a predetermined path;a pair of anode plates, one disposed on either side of saidpredetermined path and extending therealong facing said predeterminedpath, said cathode being disposed adjacent one end of said pair of anodeplates, said anode plates being spaced further apart at said one endthan at the end remote from said one end; an electron control griddisposed intermediate said cathode and said pair of anode platestransversely of said predetermined path; an electron accelerator griddisposed intermediate said electron control grid and said pair of anodeplates transversely of said predetermined path; and a pair of separateforaminous electron beam deflection grid electrodes disposed betweensaid anode plates substantially coextensive therewith, one on eitherside of said predetermined path.

10. An electron tube of the beam deflection type comprising an electrodecage including a cathode having an emitting surface facing generallyalong a predetermined path; a pair of anode plates, one disposed oneither side of said given path and extending therealong facing saidpredetermined path, said cathode being disposed adjacent one end of saidpair of anode plates, said anode plates being spaced further apart atsaid one end than at the end remote from said one end; at least one gridelectrode disposed intermediate said cathode and said pair of anodeplates transversely of said predetermined path; and a pair of separateforaminous electron deflection grid electrodes disposed between saidanode plates substantially coextensive therewith one on either side ofsaid predetermined path, each of said foraminous deflection electrodesbeing spaced further from its adjacent anode plate at said one endthereof than at said end remote from said one end.

ll. A beam deflection type electron tube comprising: an electrode cageincluding a cathode having an emitting surface facing generally along apredetermined path; a pair of anode plates spaced from each other in aV-like arrangement, each of said anode plates being disposed on oppositesides of and along said predetermined path away from said cathode withthe V thereof opening toward said cathode; an electron control griddisposed intermediate said cathode and said pair of anode platestransversely of said predetermined path; an electron aceelerator griddisposed intermediate said electron control grid and said pair of anodeplates transversely of said predetermined path; and a pair of separateforaminous electron beam deflection gridelectrodesspaced from each otherin a V-like arrangement, said pair of foraminousdeflectionelectrodesfbeing disposed substantially between said anodeplates on opposite sides of said predetermined path with the. V thereofopeningtoward said cathode, each of said foraminous deflectionelectrodes being substantially coextensive with its adjacent anodeplates, the V of said forarninous deflection electrodes being more acutethan the V of said anode plates, said electrode cage being symmetricalabout said path.,

12. An electron tube according to claim 8 and including a tubularmetallic shield member surrounding said electrode cage.

13. An electron tube according to claim 10 and including a tubularmetallicfshield member surrounding said electrode cage. 7

14.. An electron tube according to claim 11 and including a tubularmetallic. shield member surrounding said electrode cage, said shieldmember having a reentrant'portion disposed adjacent the ends of saidforaminous deflection electrodes. and said anode plates remote from saidcathode.

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